Atomic and nuclear properties of materials:
Promethium (Pm)

Quantity	Value	Units	Value	Units
Atomic number	61
Atomic mass	[144.9127]	g mole-1
Specific gravity	7.22	g cm-3
Minimum ionization	1.240	MeV g-1cm2	8.954	MeV cm-1
Nuclear collision length	103.5	g cm-2	14.34	cm
Nuclear interaction length	177.7	g cm-2	24.61	cm
Radiation length	7.51	g cm-2	1.041	cm
Critical energy	9.83	MeV (for e-)	9.49	MeV (for e+)
Molière radius	16.21	g cm-2	2.245	cm
Plasma energy	50.24	eV
Muon critical energy	180.	GeV

For muons, dE/dx = a(E) + b(E) E. Tables of b(E): PS PDF TEXT
Table of muon dE/dx and Range: PS PDF TEXT
Explanation of some entries
Note: Since there is no stable isotope, given atomic mass is that of the longest-lived known isotope as of Jan 2007.
Table of isotopes
x ray mass attenuation coefficients